Word learning is complex because it is tied to many different behaviors (looking, pointing), subserved by multiple perceptual and cognitive processes (attention, memory, categorization), and because it is extended in time. Thus, explanations of early word learning must bring together processes of visual attention, visual looking and learning, processes for tracking of what is where visual binding of what is where, and processes for the formation and updating of word-object links across contexts. And, critically, such explanations must be dynamic - able to capture how these processes work together in as children behave in the moment and how they change over learning and development. The goal of this grant is to test the first formal theory of early word learning that integrates visual object processing and word learning across multiple timescales. We build a formal computational model based on two successful extant models: the model of early word learning we developed in the last grant period, and a model of how infants visually explore their environment. The end product will be a theory that speaks to how individual children coordinate attention, visual memory, and word learning, and how these systems co-evolve over development. In four specific aims we propose 20 experiments to test model predictions, developmental hypotheses and generate data that speak to critical debates in the field. Specific Aim 1 examines the influence of words on visual exploration in space. Specific Aim 2 probes visual dynamics in tasks where children must track how often words and objects occur together. Specific Aim 3 cross-situational learning tasks examine the continuity in processes of attention and word learning in looking and reaching tasks. Finally, Specific Aim 4 extends our novel discovery from the last grant period-that children can use consistency in space to learn words-to category learning, and examine the influence of developmental changes in spatial cognitive development on word learning. The 15 proposed simulations qualitatively capture targeted findings from the literature and data from our experiments, and do so using the same parameters for related studies. The resultant theory will be poised to make extensive connections to other aspects of development including processes of preferential looking, working memory, and executive function-processes we have argued are critical for understanding how children's developing word knowledge influences in-the-moment learning. Moreover, the level at which we seek to understand these processes-the level of individual children-is a necessary step towards intervention in cases of atypical development such as SLI or prematurity55. Indeed, because our theory targets individual differences very early in word learning, the present work opens the door to future efforts using the theory to predict which infants are at risk for language delays and to use our theoretical model as a clinical tool to test candidate interventions.